Event

Processing of a visual stimulus depends on previous and surrounding stimulations. For example, how an orientation detail is perceived depends on previous and surrounding orientation content. The influence of such context, temporal and spatial, is postulated to be beneficial, but the involved mechanism(s) as well as the behavioral relevance are not fully understood. Here, using behavioral experiments that measure how context integrates in space and time, we argue that context changes how statistical decisions are made by the visual system. Most importantly, we find that several context-dependent perceptual biases, such as visual illusions and aftereffects, are much reduced with increasing reaction time. To account for this, we consider a simple yet general explanation: prior and noisy decision-related evidence are integrated serially, with evidence and noise accumulating over time (as in the standard drift diffusion model). With time, owing to noise accumulation, the prior effect is predicted to diminish. This theory suggests a single-process alternative to the intuitive notion of dual brain systems (the so-called System 1 and System 2), and quantitatively predicts several known properties of perceptual bias, such as the order-of-magnitude variation in measured bias magnitudes between individuals.